The present invention relates to an internal combustion engine, and more particularly to a failsafe system for detecting malfunctions of a device which controls the amount of fuel or intake air supplied to an engine, and for taking safety measures when a malfunction occurs.
In a device which controls the fuel injection rate employed in, or the flow rate of intake air supplied to, an engine such as a diesel engine or a spark ignition engine, a servo control system has generally been used, which uses an actuator, such as a servomotor, for the controlled device, and a detector for sensing the position or state of the controlled device to feed back a signal indicative of the state of the device to be used to further refine the controlled state of the system.
In such a servo control system, the servomotor is required to adjust rapidly to correct its speed and direction during its operation. Furthermore, it is normally mounted directly on the engine of an automotive vehicle and therefore the environment in which it is used is very severe with regard to vibrations and/or heat. Thus malfunctions due to motor seizure or interruption of electrical connection leads are liable to occur.
When such malfunctions occur in prior art control systems, the device actuated by the servomotor will suddenly be operating without proper control. It is possible in such a case for the engine speed to increase to damaging or even dangerous levels.
For example, in a system in which the fuel injection rate employed in a diesel engine is controlled by a servomotor, the starting of the engine can be reliably achieved by automatically increasing the fuel injection rate before or during the operation of the starter motor. When the servo control system including a servomotor malfunctions, however, an insufficient amount of fuel may be injected during enging starting so that the engine cannot start, or the fuel injection rate may remain increased even after the engine has entered its steady-state operation so that the engine might run at an excessively high speed.